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DOCUMENT AND ENTITY INFORMATION Document - shares
9 Months Ended
Sep. 30, 2017
Nov. 02, 2017
Entity [Abstract]    
Entity Registrant Name WESCO INTERNATIONAL INC.  
Entity Central Index Key 0000929008  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Document Type 10-Q  
Document Period End Date Sep. 30, 2017  
Document Fiscal Year Focus 2017  
Document Fiscal Period Focus Q3  
Amendment Flag false  
Entity Common Stock, Shares Outstanding   47,002,338